1. Field of the Invention
This invention relates to a measuring system comprising ion-selective sensing electrodes adjoining a measuring passage having an inlet and an outlet, which electrodes are provided at a boundary surface of that measuring passage and are flush with that surface.
Within the scope of the invention, contact and pressure contact pressure springs may be associated with all said electrodes.
Within the scope of the invention the measuring passage may extend in known manner through transparent components. This will facilitate the supervision.
2. Description of the Prior Art
A measuring system which is of the kind described first hereinbefore and comprises straight measuring passage sections is known from Published German Application Nos. 26 52 370 and 27 26 772. In said systems the measuring electrodes are screwed into their installed position. The screwed connection has the disadvantage that a uniform positioning of the electrodes relative to the measuring passage is not ensured because different tightening forces may inadvertently be exerted or because impurities which are present may have the result that the final position is not the same for all electrodes. Besides, some ion-selective electrodes are provided on their sensing surface with a protecting membrane, which may be destroyed by the sealing ring which surrounds the actual electrode surface and is clamped as the sensing electrode is screwed into position. Such destruction may result in non-uniform measurements and will reduce the utility of the system in a manner which is not readily detectable.
The measuring passage of the known system includes measuring chambers, which consist of respective recesses, which have a somewhat lower depth than the adjoining portions of the passage. That design results in a retention of the liquid to be measured in said recesses and in an irregular flow and a deflection of said liquid and may result in a separation of the flow from the sensing electrodes.
In accordance with Published German Application No. 31 16 321, hemispherical measuring chambers are provided between straight measuring passages extending along a zig-zag course. The electrodes protrude into said measuring chambers and are contacted in an undefined manner by the flowing liquid or the liquid flowing through the measuring passages may separate from the electrodes where said passages join said chambers. Even when the liquid is stagnant during the measurement, that known system will not ensure a uniform wetting of the electrodes and errors due to entrained impurities may also occur because there is no smooth flow but a retention and turbulence and there are dead spaces so that a reliable flow in contact with the electrodes and in any case a uniform flow in contact with the electrodes is not ensured. In the known system the electrodes are electrically connected to cables. This has the disadvantage that electrical interference may be detected by the sensor, i.e., the electrode, interference may be detected by the sensor, i.e., the electrode, and may be transmitted to the signal-processing circuitry.
In accordance with Published German Application No. 31 15 321, the cell which is flowed through consists of transparent material and the electrodes are axially forced against a seal by a compression spring and are thus held in position. Whereas that resilient contact pressure affords an advantage, that arrangement may not ensure an even flow in contact with the electrodes particularly when the electrode is forced against an elastic seal in an arrangement comprising straight measuring passage sections.